A study of the prevalance and severity of diabetic retinopathy is being conducted in a group of 2,400 diabetic patients in their home communities. Objective recording of the retinopathy by use of stereoscopic fundus photography combined with a standardized protocol for grading the retinopathy is being used. Grading of the stereo photographs provides a sensitive and reproducible method for the detection of the retinopathy. The frequency and causes of the visual impairment are being determined. The prevalence of retinopathy and of its various component lesions is being evaluated with respect to duration, age at diagnosis of diabetes, blood pressure level, smoking history, ponderosity, and glycosylated hemoglobin level.